Letter to the Editor
Herschel/HIFI observations of spectrally resolved methylidyne signatures toward the high-mass star-forming core NGC 6334I *,**
Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700AV, Groningen, The Netherlands e-mail: email@example.com
2 SRON Netherlands Institute for Space Research, Groningen, NL
3 California Institute of Technology, Pasadena, USA
4 Department of Astronomy, University of Michigan, Ann Arbor, USA
5 Max-Planck-Institut für Radioastronomie, Bonn, Germany
6 Physikalisches Institut, Universität zu Köln, Köln, Germany
7 Centre d'Étude Spatiale des Rayonnements, Université Paul Sabatier, Toulouse, France
8 CNRS/INSU, UMR 5187, Toulouse, France
9 Laboratoire d'Astrophysique de Grenoble, UMR 5571-CNRS, Université Joseph Fourier, Grenoble, France
10 Université de Bordeaux, Laboratoire d'Astrophysique de Bordeaux, Floirac, France
11 CNRS/INSU, UMR 5804, Floirac Cedex, France
12 Jet Propulsion Laboratory, Caltech, Pasadena, CA 91109, USA
13 Ohio State University, Columbus, OH, USA
14 Infared Processing and Analysis Center, Caltech, Pasadena, USA
15 Johns Hopkins University, Baltimore MD, USA
16 INAF - Istituto di Fisica dello Spazio Interplanetario, Roma, Italy
17 Laboratoire d'Études du Rayonnement et de la Matière en Astrophysique, UMR 8112 CNRS/INSU, OP, ENS, UPMC, UCP, Paris, France
18 School of Physics and Astronomy, University of Leeds, Leeds UK
19 Centro de Astrobiologìa, CSIC-INTA, Madrid, Spain
20 INAF Osservatorio Astrofisico di Arcetri, Florence, Italy
21 Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Amsterdam, The Netherlands
22 Department of Astrophysics/IMAPP, Radboud University Nijmegen, Nijmegen, The Netherlands
23 IGN Observatorio Astronómico Nacional, Alcalá de Henares, Spain
24 Max-Planck-Institut für Astronomie, Heidelberg, Germany
25 Harvard-Smithsonian Center for Astrophysics, Cambridge MA, USA
26 INAF - Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy
27 Institut de RadioAstronomie Millimétrique, Grenoble, France
28 Leiden Observatory, Leiden University, Leiden, The Netherlands
29 Department of Physics and Astronomy, University College London, London, UK
30 Dept. of Physics and Astronomy, University of Waterloo, Canada
31 European Space Astronomy Centre, ESA, Madrid, Spain
Accepted: 7 July 2010
Context. In contrast to the more extensively studied dense star-forming cores, little is known about diffuse gas surrounding star-forming regions.
Aims. We study the molecular gas in the Galactic high-mass star-forming region NGC 6334I, which contains diffuse, quiescent components that are inconspicuous in widely used molecular tracers such as CO.
Methods. We present Herschel/HIFI observations of methylidyne (CH) toward NGC 6334I observed as part of the “Chemical HErschel Survey of Star forming regions” (CHESS) key program. HIFI resolves each of the six hyperfine components of the lowest rotational transition (J = –) of CH, observed in both emission and absorption.
Results. The CH emission features appear close to the systemic velocity of NGC 6334I, while its measured FWHM linewidth of 3 km s-1 is smaller than previously observed in dense gas tracers such as NH3 and SiO. The CH abundance in the hot core is ~7 × 10-11, two to three orders of magnitude lower than in diffuse clouds. While other studies find distinct outflows in, e.g., CO and H2O toward NGC 6334I, we do not detect any outflow signatures in CH. At least two redshifted components of cold absorbing material must be present at –3.0 and +6.5 km s-1 to explain the absorption signatures. We derive a CH column density (NCH) of 7 × 1013 and 3 × 1013 cm-2 for these two absorbing clouds. We find evidence of two additional absorbing clouds at +8.0 and 0.0 km s-1, both with NCH ≈ 2 × 1013 cm-2. Turbulent linewidths for the four absorption components vary between 1.5 and 5.0 km s-1 in FWHM. We constrain the physical properties and locations of the clouds by matching our CH absorbers with the absorption signatures seen in other molecular tracers.
Conclusions. In the hot core, molecules such as H2O and CO trace gas that is heated and dynamically influenced by outflow activity, whereas the CH molecule traces more quiescent material. The four CH absorbing clouds have column densities and turbulent properties that are consistent with those of diffuse clouds: two are located in the direct surroundings of NGC 6334, and two are unrelated foreground clouds. Local density and dynamical effects influence the chemical composition of the physical components of NGC 6334, which causes some components to be seen in CH but not in other tracers, and vice versa.
Key words: stars: formation / ISM: molecules / ISM: individual objects: NGC 6334I
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Acknowledgements (page 5) are only available in electronic form at http://www.aanda.org
© ESO, 2010